Field of the Invention
The present invention generally relates to multi-piece golf balls and more particularly to golf balls having at least one layer made of polyamide/ionomer/fatty acid amide compositions. In one embodiment, the composition further contains a plasticizer. The golf ball includes a core having at least one layer and cover having at least one layer. For example, the ball contains an inner core and surrounding outer core layer or a multi-layered core having an inner core, intermediate core layer, and outer core layer. A polyamide homopolymer, copolymer, blend or alloy having a transparent optical nature preferably is used in the composition. Preferably, an ethylene acid copolymer ionomer is used with a plasticizer.
Brief Review of the Related Art
Multi-piece, solid golf balls are used today by recreational and professional golfers. Basically, these golf balls contain an inner core protected by a cover. The core acts as the primary engine for the ball and the cover helps provide the ball with durability and wear-resistance. The core and cover may be single or multi-layered. For example, three-piece golf balls having an inner core, inner cover layer, and outer cover layer are popular. In other instances, golfers will use a four-piece ball containing a dual-core (inner core and surrounding outer-core layer) and dual-cover (inner cover layer and surrounding outer cover layer). Intermediate (casing) layer(s) may be disposed between the core and cover layers to impart various properties. Thus, five-piece and even six-piece balls can be made. Normally, the core layers are made of a natural or synthetic rubber material or highly neutralized ionomer polymers (HNPs). These ionomer resins are typically copolymers of an olefin such as ethylene; and an unsaturated carboxylic acid such as methacrylic acid, acrylic acid, or maleic acid. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the copolymer. The acid groups may be partially or fully neutralized.
Such ethylene acid copolymer ionomer resins are relatively hard materials having good durability, cut-resistance, and toughness. The ionomers may be used to make cover, intermediate, and core layers. When used as a core material, the hard ionomer resin helps impart a higher initial velocity to the golf ball. This is particularly advantageous for driver shots off the tee. The ball tends to have good flight distance. However, one disadvantageous feature of such balls is they tend to have a hard “feel.” Some players experience a harsher, less comfortable feel when their club face makes contact with these hard balls. The player senses less control and the harder ball tends to have low initial spin. It is generally more difficult to hit hard balls with the proper touch and spin. This can be particularly troublesome when making short approach shots with irons near the green.
Also, it is generally known that increasing the neutralization of ethylene-based ionomers reduces the processability of the material in molding operations. Such highly neutralized ethylene-based ionomers have a decreased melt flow index. Thus, manufacturers of golf balls have looked at making blends of ethylene-based ionomers to improve their melt-flow and molding properties. For example, Bulpett et al., US Patent Application Publication 2010/0048327 discloses a golf ball having at least one layer made from a composition comprising a highly neutralized ethylene acid copolymer and plasticizing agent selected from an inner salt, a chelate, a surfactant, a phospholipid, an ionic liquid, a long-chain organic carbonate, a main-chain heteroatom-substituted fatty acid, and mixtures thereof. In particular, the carboxy-terminus of fatty acid analogs with one to three heteroatoms in the fatty acid moiety are modified to form various amides, esters, ketones, alcohols, alcohol esters and nitrites thereof. Polar waxes such as 12-hydroxystearamide; N-(2-hydroxy ethyl) 12-hydroxystearamide; stearamide; glycerin monostearate; sorbitan; monostearate; and 12-hydroxy stearic acid along with less polar waxes such as N,N′-ethylene-bis-stearamide; hydrogenated castor oil (castor wax), oxidized synthetic waxes, and functionalized synthetic waxes also may be used.
Sullivan, U.S. Pat. No. 5,120,791 discloses a golf ball comprising core and cover, wherein the cover comprises a blend of: i) about 10 to about 90 percent by weight of a hard ethylene acid copolymer ionomer (greater than 50 Shore D hardness and flex modulus of 15,000 to 70,000 psi); and ii) i) about 10 to about 90 percent by weight of a soft ethylene acid copolymer ionomer (20 to 40 Shore D hardness and flex modulus of 2,000 to 10,000 psi). The ionomer composition may contain 0.5-1 wt. % of a bis-stearamide wax to prevent clumping and mixing during processing.
In addition, it is known to add fatty acid amides to polyurethane compositions to improve dispersability and mold processing as described in Ichikawa et al., U.S. Pat. No. 6,833,400. In the '400 patent, a dispersant selected from a fatty acid amide, montan wax, and polyethylene wax is used, wherein the ratio of polyurethane to dispersant is in the range of 100:0.2 to 100:3.0. The resulting polyurethane composition may be used to form a golf ball cover.
Although some ionomer and polyurethane compositions may be effective for making core layers and other components in a golf ball, there is still a need for new compositions that can impart high quality performance properties to the ball. Particularly, there is a continuing need for improved core constructions in golf balls. The core material should have good toughness and provide the ball with high resiliency. The core material, however, should not be excessively hard and stiff so that properties such as feel, softness, and spin control are sacrificed. The present invention provides golf balls having an optimum combination of properties.